Back plate and driving spring for machine guns



s. G. GREEN EIAL 2,321,592

BACK PLATE AND DRIVING SPRING FOR MACHINE GUNS Filed Oct. 17, 1940 2 Sheets-Sheet 1 BY {5%. W&8MML' ATTORNEY June 15, R430 5. e. GREEN ETAL 2,321,592

BACK PLATE AND DRIVING SPRING FOR MACHINE GUNS Filed Oct. 17, 1940 2 Sheets-Sheet 2 ATTORNEY Patented June 15, 1943 BACK PLATE AND DRIVING SPRING FOR MLACHINE GUNS Samuel G. Green, Gray, Ga, and Edward W. Hopkins, Enfield, Conn.

Application October 17, 1940, Serial No. 361,596

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 3'70 0. G. 757) 4 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to us of any royalty thereon.

This invention relates to an improved back plate structure more particularly adapted, but not limited in its adaptation to any particular weapon, for use in the receiver of a machine gun of the Browning type, and being so formed and arranged as to permit the employment of a bolt return or driving spring of greater length than heretofore possible in the art.

To meet new tactical requirements it has been found essential that ammunition feed belts of greater capacity than those previously found sufficient be provided to sustain the fire of automatic weapons fed by belt for any appreciable period under the present high rate of fire required of the weapon, especially in the case of the larger caliber automatic weapons. Obviously an increase in the capacity of an ammunition belt requires greater power for advancing the loaded belt through the feedWay of the gun and it is found that the operating reserve of the conventional gun is not sufficient to advance a loaded belt of greater than conventional length through the feedway with the facility required to decrease the feeding phase time in harmony with the desired increased cyclic rate of the gun.

Although many ways have been suggested of increasing the power utilized for advancing the cartridge belt through the feedway, including a proposed rearrangement of the feed mechanism so as to employ the momentum of parts driven in recoil by the force of explosion of the ignited cartridge, it is found in service that such modifications invariably compel the introduction of features which require a non-uniform acceleration of moving parts or a decrease in the length of the camming action which in turn necessitates a decrease in advantage of the leverage system of the feed mechanism nullifying the advantage of the initial power increase.

If the smoothness of operation of the weapon is to be retained it is essential to have it feed on the counter-recoil stroke of the driving member or bolt whereby advantage of the retarded velocity and the greatest possible length of a cam track thereon for imparting uniform acceleration to a driven member may be fully exploited. This essential feature may most readily be accomplished by leaving the fundamental feeding system of the weapon undisturbed and increasing the initial loading on the driving member or bolt return spring thereby decreasing the period of the spring and correspondingly decreasing the counterrecoil travel time or phase of the bolt which of course adds a proportionate part to an increased cyclic rate of the weapon and a source of greater driving ener y, and therefore feeding energy to the feeding system actuating member or bolt. The initial loading on the driving spring is admirably adapted to be increased as the force above which is required to drive the bolt in recoil is directly utilized in compressing the driving spring with the result that the excess or reserve force arising from the force of explosion of an ignited cartridge is gainfully employed to store greater energy in the driving spring without materially increasing the recoil phase time of the bolt. In addition to providing for a greater source of driving energy for the feed system as above explained the necessity for modifying the recoil system of the gun in general is obviated inasmuch as the increased initial loading of the driving spring will relieve the buffer system of so great impact shocks as it would otherwise be subjected to with increased recoil velocity of the bolt.

It is the principal object of this invention to increase the source of energy for driving the cartridge belt feed advancing mechanism of an automatic weapon so equipped.

A further object of the invention is to utilize a greater quantity of the total available energy in an automatic weapon for driving the cartridge feed mechanism.

Another object of the invention is to arrange the bolt driving spring in a manner whereby it may be assembled in operative position in the weapon under greater initial load than heretofore.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which:

Fig. l is a fragmentary elevational view partially in section of a machine gun of the Browning type showing the present invention applied thereto;

Fig. 2 is an enlarged fragmentary View of the bolt driving spring assembly;

Fig. 3 is a top plan view of a receiver back plate conforming with the present invention and partially broken away on the line 33 of Fig. 4 to disclose the manner of securing the bolt driving spring in operative relation thereon;

Fig. 4 is a rear elevation of the receiver back plate shown in Fig. 3;

Fig. 5 is a rear elevation of a conventional receiver back plate modified in accordance with the present invention;

Fig. 6 is a side elevation partially in section of the back plate shown in Fig.

Fig. 7 is a view similar to Fig. 2 modified driving spring assembly;

Fig. 3 is a view similar to Fig. 7 showing another modification of the driving spring assembly;

Figure 9 is a partial sectional view on the line 9--9 of Figure 5.

Reference is now made to the drawings wherein the same elements are identified by the same reference characters throughout, and in particular to Fig. 1 which discloses a fragmentary portion of a machine gun of the Browning type comprising a receiver IE3 provided with a removable back plate I l, a barrel I2, bolt l3 and bolt driving spring assembly M arranged in conformity with the instant invention.

In accordance with this invention the driving spring assembly I4 is increased considerably in length over the conventional driving spring and to this end the back plate II is formed with an extension [5 which is preferably made integral with the back plate and buffer tube It as clearly shown in Figs. 1, 3 and 4, and as shown the buffer tube may also be made integral with the back plate in the manner disclosed in our copending application Serial No. 360,298, filed Ocshowing a 'tober 8, 1940. The extension i5 is formed with a longitudinal through bore as indicated at I? which is disposed in parallelism with the axis of the buffer tube and serves to receive the rear end portion of the driving spring assembly H! as hereinafter more particularly set forth.

As clearly shown in Fig. 2 the driving spring assembly It comprises a driving spring rod it having a forward portion 4 9 of enlarged diameter defining an annular shoulder 23 at its junction with the body of the rod. A locking head 2| provided with laterally projecting finger pieces 22 and circumferentially spaced locking lugs 23 is suitably secured to the rear end portion of the driving spring red as by being formed with a socket to receive the rear end portion of the rod and being pinned to the rod in socketed relation as by the transverse pin 24. The forward end of the locking head forms a spring seat 25 for the rear end of a driving spring organization which in view of the unusual length thereof in the instant case is conveniently comprised of a plurality of sections indicated at 26 and 2?, respectively, to facilitate manufacture thereof and obviate the well known "buckling characteristics inherent in a long spring under load. Collars 28 are interposed between the adjacent ends of the spring sections 25 and 27 and the forward end of spring section 21 and shoulder 20 which serve to form seats for the spring sections and as will hereinafter appear, properly guide the driving spring rod within the bolt recess 29 therefor as indicated in Fig. 1.

Where it is desired to modify the conventional back plate to coact with a driving spring assembly of greater than conventional length as herein disclosed, such modification may advantageously be effected as shown in Figs. 5 and 6 wherein a tubular member 3%! having spaced lugs 3| formed with arcuate seats is secured to the buffer tube in axially parallel relation as by welding and is functionally the full equivalent of the extension Hi. The tube 30 is also welded adjacent its forward end to the back plate around the junction with the bore 3210 increase the security of the attachment of the tube to the back plate and to render the joint fluid tight.

The rear end portion of the bore ll of Figs. 3 and 4 or the rear end portion of the interior of tube 30 of Figs. 5 and 6, as the case may be, is provided with spaced bayonet type grooves 33 to receive the corresponding locking lugs 23 on the driving spring locking head 2i. To facilitate machining of the grooves the circumferentially disposed portions thereof may be joined in a continuous grooveway originating at the surface of the bore or interior of the tube and increasing in depth either clockwise or counterclockwise to a desired uniform depth. By arranging the least depth of the latter groove portions in proper relative relation to the longitudinal portions of the bayonet grooves an operator will be compelled to rotate the locking head 2| in a predetermined direction to effect interlocking of the lugs 23 with its cooperating counter elements of the bayonet grooves whereby retaining means may be employed in fixed relative relation to the bayonet grooves for retaining the locking head 2'! in interlocked relation therewith. In the instance illustrated the circumferential groove portions of the bayonet grooves are so arranged as to compel clockwise rotation of the locking head 2| as viewed in Fig. 5.

In either form of the invention the retaining means for retaining the locking head in interlocked relation with the bayonet grooves comprises a stop pin 34 affixed to the rear face of the extension i5 or rearmost lug 3| and so positioned as to be engageable with the adjacent finger piece 22 of the locking head to limit clockwise rotation thereof as viewed in Figs. 4 or 5. A plunger 35 reciprocable in axially parallel relation to the bore H or tubular member 30 is mounted in the rear end portion of extension #5 or rearmost lug 3! in such manner as to be normally engageable with the finger piece of looking head '2! remote from the finger piece engageable with stop pin 34 to prevent counterclockwise rotation of the locking head 2| from interlocked relation with its coacting bayonet grooves.

The plunger 35 may conveniently be urged to its normal position, wherein it abuts a stop pin 36 arranged to permit reciprocable movement of the plunger, by resilient means such as the spring 31.

In operation the gun will be assembled, as in normal cases except as to the back plate and driving spring assemblies. The latter assembly will be effected by mounting a colla 23 upon the driving spring rod so as to engage the annular shoulder 20, the spring section 21 will next be mounted upon the rod followed by the second and floating collar 28 and spring section 26. The spring sections 23 and 2! are of such length as to exceed in their unloaded condition, the length of the driving spring rod and such length is so chosen as to prevent loading of the springs to solid height in operation of the gun as well as to compel an initial loading in accordance with predetermined design in order to secure the locking head 2| to the driving springrod. Upon completion of mounting the spring sections 26, 21 and collars 23 upon the driving spring rod the springs are compressed to permit attachment of thelocking head 2! to the rear end of the driving spring rod as by the transverse pin 24 which operation initially loads the driving spring sections as desired and completes assembly of this organization. Contrariwise to the normal method of assembly of the gun the back plate H in the present case is assembled on the receiver side plates 'before the driving spring assembly is mounted in operative relation. After the back plate is mounted on the receiver side plates the driving spring assembly is inserted through the bore I! or tubular member 36 with the enlarged end portion [9 forwardmost and positioned Within the bolt recess 29 With the forward collar 28 abuttin the abutment 38 therein and the enlarged end portion projecting forwardly of the bolt and, supportably seated within a recess 39 in the barrel extension 40. The driving spring assembly is locked to the extension or tubular member by inserting the locking lugs 23 through the coacting longitudinal groove portions of the bayonet grooves 33, which will cause the adjacent finger piece of the locking head to depress plunger and permit clockwise rotation of the assembly to effect interlocking of the lugs 23 with the counterparts of the grooves in which position rotation will be limited by the stop pin 34. Upon completion of the locking opera tion the plunger 35 will be projected by its spring 31 into the path of counterclockwise movement of the locking head 2| to restrain the head to interlocked relation. The collars 28 will function to eliminate whip of the driving spring and otherwise serve to guide the bar upon relative movement of the bolt with respect thereto.

Fig. 7 discloses a modified form of driving spring assembly similar to Fig. 2 having a driving spring rod l8 similar to, but of smaller diameter than, the rod 18 so that an abutment 25 on the locking head 2| and collars 28' of greater width may be obtained. The enlarged end IQ of the rod is the same in all respects as the head 19 of rod l8. tions 26' and 21 are each comprised of right and left hand springs of such diameter that they may be disposed one in the other and upon the rod 18 to seat upon the abutment 25 and adjacent collar 28 or upon both the collars 28' as the case may be. By this expedient the initial load may be greatly increased as above explained in connection with the form shown in Fig. 2.

In the modification of Fig. 8 the driving spring rod l3", enlarged end portion l9" thereof, looking head 2 l and collar 28 adjacent the enlarged end is" of the rod are the same as in Fig. 7. The driving springs 25" and 21" are continuous right and left hand helical springs such as the springs constituting the sections 26' and 21' but extend from the locking head 2 I to the endmost collar 28 with the intermediate collars 28 or 28 omitted. Where double springs are utilized omission is permissible since they coact to mutually intersupport each other and reduce buckling.

While We do not limit the invention to any precise increase in length of the driving springs I have found that a 20% increase in length of the driving springs over those heretofore used, thus permitting a 100% increase in the initial loading thereof, is feasible by the expedient herein disclosed and will accomplish the objects sought.

As in the copending application above referred to the buffer discs may be comprised of Rayon fabric impregnated with Duprene or similar synthetic rubber.

Having now described a present preferred embodiment of the present invention we claim:

1. In a machine gun, a receiver, a back plate for the receiver, an extension secured to the back plate and provided with a longitudinal bore communicating with the interior of the receiver, a

In this instance, however, the spring secdriving spring rod, a driving spring on said rod, a locking head on the rear end of the driving spring rod, and means for releasably locking the locking head to said extension, said means for releasably locking the locking head to said extension comprising locking lugs on said head, coacting bayonet grooves within said bore of the extension, a stop pin secured to the extension for limiting rotary movement of the head in one direction and a plunger for normally limiting rotary movement of the head in a contra direction depressible to permit rotation of the head secured to said extension.

2. In a gun, a bolt driving assembly comprising in combination, a driving spring rod, a seat adjacent one end of the rod, a locking head having spaced locking elements and laterally extending finger pieces, said locking head being secured to the end portion of the driving spring rod remote from said seat, a resilient driving element mounted upon said rod and confined between said seat and locking head under an initial load, complementary locking elements on the gun for receiving the first recited locking elements in interlocked relation, and means on the gun engageable with said finger pieces for releasably holding said locking elements in interlocked relation.

3. In a gun, a bolt driving spring assembly comprising a driving spring rod having a portion at one end of enlarged diameter defining an annular seat at its junction with the body of the rod, a locking head of generally cylindrical shape having circumferentially spaced locking lugs and finger pieces projecting laterally at one end, said locking head being formed with an axially disposed socket on its end portion remote from said finger pieces adapted to receive the end portion of the driving spring rod remote from said shoulder, means securing the driving spring rod in socketed relation to said locking head, a driving spring mounted upon the driving spring rod and confined between said annular seat and the confronting end of the locking head under initial compression, complementary locking lugs on the gun for engaging the first recited lugs in interlocking relation, and means on the gun engageable with said finger pieces for releasably holding said lugs in interlocked relation.

4. In combination, a driving spring assembly, a back plate having a bore therethrough sufficiently large to receive said driving spring assembly, an elongated extension longitudinally bored on the same diameter as said first recited bore secured to the back plate in rearwardly extending direction with said bores defining continuations of each other, and means on said extension and driving spring assembly for releasably interlocking the driving spring assembly in the bore of said extension and adapted to permit rearward withdrawal of said driving spring assembly from the extension, said means comprising bayonet grooves formed in the end portion of the bore of said extension remote from the back plate adapted to receive complementary locking lugs on said driving spring assembly in combination with a spaced stop pin and plunger adapted to selectively control rotation of the driving spring assembly in relation to the exten-v sion.

SAMUEL G. GREEN. EDWARD W. HOPKINS. 

